Exhaust-gas turbochargers are widely used in series motor vehicles in order to increase the performance of the respective vehicle engines. It is advantageous that the engines can be configured with small cubic capacity and comparably small measurements so that the internal friction in the engine remains minimal and favourable degrees of efficiency can be achieved already on this basis alone.
According to the conventional manner of construction today, the exhaust-gas turbochargers have a rotor with a compressor wheel and a turbine wheel and a shaft arranged between said compressor wheel and turbine wheel, said shaft being rotatably mounted on the turbine side and on the compressor side with corresponding rotor bearings. The rotor bearings are customarily slide bearings with oil lubrication, the housing of the bearing on the turbine side being sealed on the side opposite the turbine wheel by means of piston rings that are arranged in corresponding piston ring grooves on the shaft or on a shaft part. By means of the preferably doubly arranged piston rings, an escape of the lubricating oil from the bearing housing in the direction of the turbine wheel is intended to be prevented.
This is important because the turbine wheel attains high temperatures during the operation of the exhaust-gas turbocharger and the lubricating oil possibly escaping in the direction of the turbine wheel can change into coke owing to the high temperatures.
Document EP 1 002 935 A1 shows the features of the preamble of claim 1. The intermediate piece is configured from many different views, two layers being designed as cylindrical sections, so that the cross-section available there for heat transfer is correspondingly reduced.
Document DE 10 2004 025 049 A1 shows a turbocharger the turbine wheel of which is connected in a rotationally fixed manner to the compressor wheel by means of a shaft, a heat-conducting throttle, which is characterised as “heat insulating”, being available in the shaft between a shaft part that is on the turbine wheel side and a shaft part that is on the compressor wheel side.
Document WO 2008/071253 A1 relates to a special manner of constructing the rotor of a turbocharger. In a basically known manner, the rotor has a shaft axially arranged between a compressor wheel and a turbine wheel, said shaft connecting the two wheels to one another in a rotationally fixed manner. The turbine wheel is arranged on a connection pin continuing the shaft on the turbine wheel side, the connection plane of the shaft and the connection pin being axially distanced from the compressor-side front face of the turbine wheel. This is intended to ensure that there is sufficient space present on the connection pin for piston ring grooves and that they can be arranged inside the material provided for the turbine wheel that has an increased heat resistance in comparison to the shaft.
Document EP 0 513 646 B1 discloses a method for connecting steel parts to aluminium- or titanium-alloy parts. This method is particularly suited for connecting the compressor wheel of a turbocharger to the rotor wheel. In this manner, it is possible to connect a compressor wheel composed of aluminium- or titanium-alloy parts to the rotor wheel that is manufactured of steel in the light of the thermal stress created by the turbine wheel. According to document EP 0 513 646 B1, it is provided for the connecting of parts composed of steel with such parts manufactured of aluminium-alloy, that a pure nickel layer be applied to the steel by means of friction welding and to connect the worked surface with the aluminium alloy by means of friction welding. In order to connect parts composed of steel with such parts manufactured of titanium alloy, it is analogously provided that a copper layer be applied on the steel by means of friction welding and that a vanadium layer be applied to the titanium alloy by means of friction welding, and connected the worked copper and vanadium surfaces by means of friction welding. As a result, highly stresses machine elements composed of very different materials can be welded together.
Document WO 2008/071253 shows a connection between turbine wheel and rotor wheel, a substantially tubular connection pin being arranged or integrally formed on the front face, which is opposite the rotor shaft, of the turbine wheel, said connection pin having in comparison to the exterior diameter of the RS a large exterior diameter and being connected on it axial end that is on the shaft side to an annular step of a connection part that is arranged or integrally formed on the RS, a hollow space remaining on the interior of the tubular connection pin the axial length of which corresponding to approximately the axial length of an external circumferential zone provided on the external circumference of the connection pin for two adjacent piston ring grooves.
In this manner, a high degree of stability is intended to be ensured in the transition zone between RS and turbine wheel in the region of the piston ring grooves.
Document DE 10 2005 015 947 B3 relates to a friction welding process for the rotor of a turbocharger, with which components composed of steel and metal aluminide can be connected. In the instance of a rotor of a turbocharger, the turbine wheel can then consist of a metal aluminide and be connected to a RS consisting of steel.
A fundamentally similar method is the subject matter of document WO 98/45081. Here, a turbine wheel composed of a titanium aluminide is intended to be connected to a RS of a turbocharger, which RS is composed of steel. In order to make this possible in terms of welding technology, a multi-layer intermediate body is axially inserted between the RS and the turbine wheel.